EP0504011B1 - Procedure for obtaining an article in a transparent polymer with a refractive index gradient - Google Patents

Description

The present invention generally relates to obtaining an article of transparent polymer material with a refractive index gradient, the refractive index varying therein continuously in at least one direction.

It relates more particularly, but not necessarily exclusively, to the case where such an article is capable of being used for the production of an ophthalmic lens.

As is known, the variation of the refractive index within an ophthalmic lens allows, for example, with equal correction, to reduce, if desired, the maximum thickness, and therefore the weight, to benefit of user comfort.

Various methods have already been proposed for obtaining a refractive index gradient in a polymer material.

For example, and this is particularly the case in American patent US-A-3,718,383, it is possible to ensure absorption, in practice by diffusion, by the polymer material, in this case hardened, of an additive composition ; in practice a thinner.

Alternatively, and this is the case in Japanese patent document No. 60-175009, it is possible to intervene on a gel, with a monomer capable of leading to a polymer with a refractive index different from that of the base material, then ensuring final polymerization of the assembly to fix the geometry of the gradient-refractive index then obtained.

However, this geometry depends directly on the concentration profile of the monomer within the basic polymer material.

It therefore depends on the monomeric polymer interaction and it can therefore be at least partly influenced by the temperature changes which may occur during diffusion.

However, it is difficult, under these conditions, to precisely control the spatial distribution of the refractive index gradient obtained.

In addition, the distance over which it is possible to obtain a refractive index gradient, which corresponds to the distance of diffusion of the monomer in the material base polymer, is, in both cases, limited.

To obtain precise control of the spatial distribution of the refractive index gradient, it has also been envisaged to diffuse a mixture of monomers in a gel, to vary the composition of this mixture over time during diffusion. until obtaining a relative concentration profile corresponding to the desired refractive index gradient profile, and then completing the polymerization of the assembly to fix the geometry thus obtained for the refractive index gradient.

But, if, for the rest, this method is satisfactory, it also does not make it possible to extend significantly the distance over which a gradient of refractive index can thus be obtained, this being still limited by dissemination practiced.

The present invention generally relates to a method for overcoming this difficulty, and for controlling and controlling the spatial distribution of the gradient of refractive index obtained.

This process, which therefore aims to obtain an article made of transparent polymer material with a refractive index gradient, is of the type according to which the absorption, by the polymer material, of an additive composition containing at least one monomer capable of leading to a polymer with a refractive index different from that of the base polymer material, and it is generally characterized in that, choosing a swelling composition for the additive composition, a first geometry is produced, a first preform made of basic polymer material with a rate of advance sufficient for this first preform to be self-supporting, a confinement volume is defined between this first preform and a stop element having a second geometry which, at least in part different from the first, corresponds to a volume greater than that to which it corresponds, we put in contact, in this confinement volume, said pre preform, with a sufficient amount of the swelling additive composition for the swelling which it is then the object leads it to marry under constraint said second geometry, the polymerization of the resulting polymer material is ensured, and, if necessary, the second preform thus obtained is surfaced at the final geometry desired for the article sought.

In short, by buttressing, according to the invention, the swelling of which the treated polymer material is the object, a swelling gradient is created in the part concerned thereof which essentially results in the refractive index gradient research.

Now, this swelling gradient itself only depends on the difference between the two geometries between which the swelling develops from one preform to the other.

Thus, the spatial distribution of the refractive index gradient obtained within the second preform only depends on this geometry differential.

It is therefore possible, according to the invention, to obtain any gradient profile of refractive index over all or part of the article concerned.

It suffices to choose accordingly the two geometries to be implemented.

In addition, with the swelling gradient set up according to the invention, and contrary to what is obtained with the diffusion methods of the prior art described above, the refractive index gradient advantageously develops in a direction transverse to that along which this swelling is established.

In practice, this is a radial direction for the article concerned.

Be that as it may, there is therefore no longer a limit as to the distance over which the effects of the gradient of refractive index obtained can extend.

As before, it suffices to choose the two geometries used accordingly.

Finally, it is at least theoretically possible, according to the invention, and tests confirm it, to ensure that the refractive index gradient is only due to swelling.

Throughout any straight line parallel to the direction in which the corresponding swelling gradient has developed, the refractive index is then advantageously constant.

In all cases, the maximum difference in refractive index that it is possible to obtain with the process according to the invention depends, on the one hand, on the refractive index of the basic polymer material and on that of the swelling additive composition, and, on the other hand, the maximum swelling rate of this basic polymer material vis-à-vis this swelling additive composition.

It is therefore sufficient to choose one and the other of these materials accordingly.

• la figure 1 est une vue en perspective d'un article en matériau polymère transparent à gradient d'indice de réfraction à la réalisation duquel peut être appliquée l'invention ;
• la figure 2 est une vue en coupe se rapportant à la réalisation préalable d'une première préforme de cet article ;
• la figure 3 est une vue en coupe de la préforme correspondante ;
• la figure 4 est une vue en coupe correspondant à la réalisation d'une deuxième préforme de l'article recherché ;
• la figure 5 est une vue en coupe de cette deuxième préforme, telle que supposée polymérisée in situ avant d'avoir atteint un équilibre de gonflement total ;
• la figure 6 est une vue en coupe de l'article recherché, tel que supposé obtenu après un surfaçage approprié de la deuxième préforme précédente ;
• les figures 7 et 8 sont des diagrammes se rapportant à cet article ;
• les figures 9, 10, 11 et 12 sont des vues en coupe axiale qui, analogues à celle de la figure 5, se rapportent chacune respectivement à des préformes auxquelles correspondent des distributions spatiales de gradient d'indice différentes de celle à laquelle correspond la préforme représentée sur cette figure 5 ;
• la figure 13 est un diagramme récapitulatif de ces distributions spatiales de gradient d'indice ;
• la figure 14 est une vue en coupe analogue à celle de la figure 4, pour une variante de mise en oeuvre.

The characteristics and advantages of the invention will become apparent from the description which follows, by way of example, with reference to the appended schematic drawings in which:

• Figure 1 is a perspective view of an article of transparent polymeric material with a refractive index gradient to which the invention can be applied;
• Figure 2 is a sectional view relating to the prior production of a first preform of this article;
• Figure 3 is a sectional view of the corresponding preform;
• Figure 4 is a sectional view corresponding to the production of a second preform of the desired article;
• Figure 5 is a sectional view of this second preform, as assumed polymerized in situ before having reached a total swelling equilibrium;
• Figure 6 is a sectional view of the desired article, as assumed obtained after appropriate surfacing of the second previous preform;
• Figures 7 and 8 are diagrams relating to this article;
• Figures 9, 10, 11 and 12 are views in axial section which, similar to that of Figure 5, each relate respectively to preforms to which correspond spatial distributions of gradient index different from that to which the preform corresponds shown in this figure 5;
• FIG. 13 is a summary diagram of these spatial distributions of index gradient;
• Figure 14 is a sectional view similar to that of Figure 4, for an alternative embodiment.

These FIGS. 1 to 14 illustrate by way of example the application of the invention to obtaining an ophthalmic lens 10 shown in isolation in FIGS. 1 and 6.

Overall, to obtain this, absorption is ensured, by a transparent base polymer material, and according to methods described in more detail later, of an additive composition containing at least one monomer capable of leading to a polymer with an index of refraction different from that of the base polymer material.

In doing so, and according to the invention, a swelling composition is chosen for the additive composition.

In practice, the choice of the couple of basic polymer material, on the one hand, swelling additive composition containing at least one monomer, on the other hand, must preferably meet the following requirements:

First of all, and by definition, the basic polymer material must be swellable under the action of the swelling additive composition, at least to a sufficient extent for carrying out the process according to the invention.

Preferably, but not necessarily necessarily, the base polymer material and the swelling additive composition are chosen so that the base polymer material has a swelling of at least 100% in the swelling additive composition.

In addition, the final polymeric material must be transparent.

Finally, in order to obtain a significant refractive index gradient, there must exist, between the basic polymer material and the polymer corresponding to the swelling additive composition, a minimum difference in refractive index.

Preferably, the basic polymer material and the swelling additive composition are chosen so that this difference in refractive index is at least equal to 0.005.

For example, the basic polymer material comprises a polyolefin.

More specifically, it can for example be such a polyolefin.

Preferably, it is then mainly formed of styrene, and the corresponding swelling additive composition essentially contains methyl methacrylate.

The corresponding swelling rate G is 100%, and the maximum difference Dmax that can be obtained for the refractive index is of the order of 0.05.

Preferably, the basic polymer material is added with crosslinking agent, such as for example divinylbenzene, or triethylene glycol dimethacrylate (by abbreviation: TEGDM), at a rate, in this case, of 0.5%.

Likewise, the swelling additive composition is preferably added with crosslinking agent, such as for example TEGDM.

Preferably, also, the basic polymer material also contains a product, which, such as for example allylmethacrylate, at a rate, in this case, of 10%, is capable of linking its network to that of the additive composition, for the obtaining, for the final polymer material obtained, a semi-RPI type network, that is to say a network, which, while being similar to interpenetrating polymer networks, comprises chemical bonds between the polymers which constitute it.

Table I below gives a specific example for such a pair of base polymer material and swelling additive composition, with the corresponding results.

The rates in brackets in this table I are appreciated with respect to a rate of 100% for styrene and are mass rates.

As a variant, the basic polymer material can comprise a polyurethane.

More specifically, it can for example be such a polyurethane.

For example, it then results for the most part from the reaction of a composition comprising at least one isocyanate and at least one polyol, and the corresponding swelling additive composition then essentially contains styrene.

Table II below gives specific examples of such a pair of base polymer material and swelling additive composition, with the corresponding results.

IPDI

: isophorone diisocyanate fabriqué par HULS

U 1004 *

: polyetherdiol fabriqué par UGINE-KUHLMANN

T 301 *

: polyester triol fabriqué par UNION CARBIDE

HEMA

: hydroxy éthyl méthacrylate

HDT *

: triisocyanatohexyle isocyanurate fabriqué par RHONE-POULENC

DBLE

: dibutyldilaurate d'étain

CAPA 200 *

: polyesterdiol fabriqué par la Sté SOLVAY

DESMODUR W *

: diisocyanate de dicyclohexyle méthane fabriqué par BASF

DESMODUR N 100 *

: triisocyanatohexyle biuret fabriqué par BASF.

* : Marque commerciale.In Table II, the abbreviations have the following meanings:

IPDI

: isophorone diisocyanate manufactured by HULS

U 1004 *

: polyetherdiol manufactured by UGINE-KUHLMANN

T 301 *

: polyester triol manufactured by UNION CARBIDE

HEMA

: hydroxy ethyl methacrylate

HDT *

: triisocyanatohexyle isocyanurate manufactured by RHONE-POULENC

DBLE

: tin dibutyldilaurate

CAPA 200 *

: polyesterdiol manufactured by SOLVAY

DESMODUR W *

: methane dicyclohexyl diisocyanate manufactured by BASF

DESMODUR N 100 *

: biuret triisocyanatohexyle manufactured by BASF.

* : Trademark.

In addition, the figures indicated in brackets in Table II correspond to the proportions of the isocyanate reactive functions, on the one hand, and alcohol, on the other hand.

Finally, in Table II, and like the preceding allylmethacrylate, hydroxyethyl methacrylate (by abbreviation: HEMA), or isocyanatoethyl methacrylate, constitute products capable of connecting the network of the base polymer material to that of the swelling additive composition [V. NEVISSAS, J.M. WIDMAYER and G.C. MEYER (CRM de STRASBOURG), Journal of Applied Polymer Science, vol. 36, 1467-1473 (1988)].

According to another variant, the basic polymer material can comprise both a polyurethane and a monomer, not polymerized at this stage, of the allylic type.

The swelling additive composition then essentially contains styrene.

Table III below gives a specific example of such materials, with the corresponding result, and under the same conditions as above.

TBPIN

: terbutylperoxy triméthylhexanoate fabriqué par SCPO

XR80 *

: diallylcarbonate de diéthylène glycol fabriqué par RHONE-POULENC.

* : Marque commercialeIn this table III, the abbreviations have the following meanings:

TBPIN

: terbutylperoxy trimethylhexanoate manufactured by SCPO

XR80 *

: diethylene glycol diallylcarbonate manufactured by RHONE-POULENC.

* : Trademark

It should also be emphasized that, the basic polymer material comprising, as indicated, in addition to a polyurethane, an allyl monomer, in a first step, the polyurethane network is formed, the allyl monomer present in the medium being intended to react during the final polymerization, after swelling.

The first preform is therefore, in this case, a polyurethane network impregnated with allyl monomer.

This allylic monomer makes it possible to increase, after its polymerization, the mechanical properties of the second preform, and therefore of the final article obtained.

In view of the above, it should also be emphasized that the refractive indices to which reference is made in the present application are those of the polymers taken in their final state, that is to say after the final polymerization having led to the desired article, and that it is in a broad sense that the term "basic polymeric material" should be extended in the present application.

According to another variant, the basic polymer material comprises both a polyurethane and an acrylic or methacrylic monomer playing the same role as the allylic monomer of the previous variant.

Table IV below illustrates this possibility, under the same conditions as above.

We will now give, with reference to FIGS. 1 to 6, practical methods of carrying out the invention.

First of all, FIGS. 2 and 3 produce a first preform P1 made of basic polymer material with a rate of advance sufficient for this first preform P1 to be self-supporting.

For example, the basic polymer material is prepared by reacting, in a mold 11 formed from two molding shells 12, 12 ′ and an annular seal 13 bracing them, the following composition, which falls under Table II above:
HDT (1)
CAPA 200 (0.9)
HEMA (0,1)

There is a priori no link between the geometry G1 to be given to the first preform P1 to be implemented and that G0 sought for the desired ophthalmic lens 10, except, of course, actually allowing the latter to be obtained.

In the example of application shown, the ophthalmic lens 10 is a concavo-convex lens, of optical axis XY, and of geometry G0 formed essentially of two surfaces S0, S′0, one convex, l other concave.

By way of example 1, and as shown, the first preform P1 sought is then for example biconvex, with a geometry G1 formed by two convex surfaces S1, S′1.

For example, the thickness at the center E1 of this preform P1 is 10 mm, its thickness E2 along its edge is 5 mm, its diameter 2R is 80 mm, and the radius of its convex surfaces S1, S ′ 1 is 254 mm.

The mold 11 is established accordingly.

It therefore has, internally, the geometry G1.

Preferably, it is added, as a catalyst, in the composition placed in this mold 11, DBLE, at a rate of 0.1%, and the whole is brought from 42 ° C to 80 ° C in 10 h , to then be kept at 80 ° C for 4 h.

In the basic polymer material then constituting the first preform P1 thus obtained, the rate of advancement is of the order of 100%.

As a variant, it could be between at least the rate of progress when the gel is set in the material and 100%.

In general, it suffices that it allows the first preform P1 obtained to be self-supporting.

Anyway, the refractive index of the corresponding transparent polymer material is 1.5.

According to the invention, a confinement volume 14 is generally defined then between this first preform P1 and at least one abutment element 16, 16 ′ having opposite it a second geometry G2 which, at least in part different from the first geometry G1, corresponds to a volume greater than that to which it corresponds.

For example, and as is the case in the embodiment more particularly shown in FIG. 4, this first preform P1 is placed in a confinement enclosure 15.

For example, and as shown, this confinement enclosure 15 is, like the mold 11, constituted, on the one hand, by two walls 16, 16 ′, each of which constitutes a stop element 16, 16 ′, and , on the other hand, an annular seal 17 bracing these walls 16, 16 ′.

In the embodiment more particularly shown, the walls 16, 16 ′ are each made up of flat plates with internal surfaces S2, S′2 perpendicular to the optical axis XY and spaced from each other by a distance which, in this embodiment, is equal to the thickness at the center E1, or 10 mm, of the first preform P1.

As shown schematically by arrows F, F ′, the walls 16, 16 ′ are duly butted, for example by a flange not shown.

According to methods which, pertaining to those skilled in the art, will not be described here, the first preform P1 is brought into contact, in the confinement volume 14 defined by this confinement enclosure 15, with the retained swelling additive composition. .

In this case, it is styrene supplemented with 1% TEGDM, and, as catalyst, 0.5% azobisisobutyronitrile.

The refractive index of the polymer corresponding to this swelling additive composition is 1.59.

In practice, the swelling which is then the object, at room temperature, the first preform P1, in contact with this swelling additive composition, lasts four days.

In practice, too, the quantity of swelling additive composition used is sufficient for this swelling to lead this first preform P1 to closely match, under stress, the second geometry G2 defined by the abutment elements 16, 16 ′ that constitute the walls 16, 16 ′ of the confinement enclosure 15, everything happening as if its convex surfaces S1, S′1 then applied at any point to the corresponding plane surfaces S2, S′2.

The resulting polymer material is then polymerized, by subjecting the assembly to a heating cycle during which the temperature is raised to 100 ° C.

Of course, this polymerization, carried out in situ, must take place before the total swelling equilibrium is reached, so that there is effectively a swelling gradient within the material treated.

It is in this sense that it is specified that the second preform P2 sought applies under stress to the corresponding stop elements 16, 16 ′.

Because of this application, the second preform P2 thus obtained, FIG. 5, effectively has a second geometry G2 which is like that defined by these abutment elements 16, 16 ′.

It is therefore, in this case, a puck of flat surfaces and circular contour, the seal 17 also constituting for its part a stop element.

To better materialize the invention, there has been shown, in broken lines, in Figure 5, in this puck, the geometry G1 of the initial preform P1.

In Figure 7, is shown, depending on the radius R, the swelling G occurred between the first preform P1 and the second preform P2.

Taking into account the practical methods of execution, this swelling G is zero along the optical axis XY, and then increases radially on either side of it, until it is maximum at the periphery.

In this case, taking into account the initial thickness E1 of the first preform P1 along its edge, this maximum swelling is 100%.

The diagram in FIG. 8 gives, as a function of the radius R, the profile of the refractive index N, as obtained after swelling and polymerization.

On the XY optical axis, this refractive index is of the order of 1.5.

At the periphery, it is around 1.55.

In a third step, when, as in the present case, this is necessary, the second preform P2 previously obtained is surfaced at the final geometry G0 desired for the ophthalmic lens 10 sought.

FIGS. 9 to 12 relate to preforms P2 which, by way of example, all have the same geometry G2 as the previous preform P2, but to which correspond spatial distributions of different refractive index, the preforms P1 from which they come, shown in dashed lines, having different geometries G1 but retaining the same diameter 2R equal to 80 mm.

In FIG. 9, example 2, the preform P1 is biconvex but its convex surfaces S1, S′1 simply have a radius different from that of the previous convex surfaces S1, S′1.

For example, this radius is 321.25 mm, the thickness in the center of 10 mm and the thickness along the edge of 5 mm.

In FIG. 10, example 3, the preform P1 is biconcave.

For example, the radii of the corresponding concave surfaces are each 321.25 mm, the thickness in the center is 5 mm and the thickness along the edge 10 mm.

In FIG. 11, example 4, the preform P1 is plano-convex.

For example, the radius of the corresponding convex surface is 110.41 mm and the thickness along the edge is 2.5 mm.

Finally, in FIG. 12, example 5, the profile of the surfaces S1, S′1 of the preform P1 has an inflection point.

For example, these surfaces S1, S′1 have the same profile, they are convex in their central zone, their radius in this central zone is 134.08 mm, the radius of the concave zone of their profile is 81.25 mm, the thickness in the center is 10 mm, and the thickness along the edge is 2 mm.

The diagram in FIG. 13 gives the profile of the corresponding refractive indices N, as obtained after swelling and polymerization.

In this diagram, the curve N2 corresponds to example 2, the curve N3 to example 3, the curve N4 to example 4 and the curve N5 to example 5.

In the variant implementation illustrated in FIG. 14, the confinement volume 14 only intervenes locally, thanks to a local depression, provided for this purpose, of the surface S1 of the preform P1.

This confinement volume 14 is then in practice defined between this preform P1 and a molding shell 16, which, constituting the corresponding stop element 16, moreover follows the shape of the surface S1.

Of course, this molding shell 16 must, as before, be butted, or, more generally, be fixed relative to the part of the surface S1 of the preform P1 not concerned by the corresponding confinement volume 14.

Of course, also, the present invention is not limited to the examples thus described and shown, both with regard to the geometries used and with regard to the materials used.

The present invention is not limited either to the practical methods of implementation explained, but extends to any variant.

In particular, to homogenize the mechanical properties of the final polymer, it is possible to ensure that it also develops a certain swelling along the optical axis.

It suffices to space the first preform P1 the abutment elements 16, 16 ′ that constitute the walls 16, 16 ′ of the confinement enclosure 15, by providing for this first preform P1 spacing means specific to its maintenance between these walls 16, 16 ′.

For example, the swelling along the optical axis XY can then be 100%, and that along the periphery can be of the order of 200%.

In addition, instead of acting on one and the other of the surfaces of the first preform, the swelling may just as well occur on one of these surfaces.

This can in particular be the case for obtaining a semi-finished ophthalmic lens already having on one of its surfaces the required geometry.

Similarly, if in the foregoing, provision has been made to develop swelling for the entire polymer material basic, this swelling may just as well affect only part of it.

Finally, although this is the case in the example explained, one and / or the other of the two successive preforms does not necessarily have a symmetry of revolution.

Claims (10)

1. A process for producing an article of transparent polymer material with a refractive index gradient, of the kind comprising effecting absorption by the basic polymer material of an additive composition containing at least one monomer capable of resulting in a polymer with a refractive index different from that of the basic polymer material, characterised in that, selecting a swelling composition for the additive composition, a first preform (P1) is produced, in accordance with a first geometry (G1), of basic polymer material with a degree of advancement sufficient for said first preform (P1) to be self-supporting, a confinement volume is defined between said first preform (P1) and an abutment element having facing same a second geometry (G2) which, at least in part different from the first, corresponds to a volume greater than that to which the first corresponds, said first preform (P1) is brought into contact in said confinement volume (14) with a sufficient amount of the swelling additive composition for the swelling action of which it is then the object to cause it to adopt said second geometry (G2) in a stressed condition, polymerisation of the resulting polymer material is effected and if necessary the second preform (P2) which is obtained in that way is surfaced to the final geometry (G0) desired for the required article (10).
2. A process according to claim 1 characterised in that, for defining the confinement volume (14), the first preform (P1) is disposed in a confinement enclosure of which one at least of the walls constitutes an abutment element.
3. A process according to either one of claims 1 and 2 characterised in that the basic polymer material and the swelling additive composition are so selected that the difference in refractive index between the basic polymer material and the polymer corresponding to the swelling additive composition is at least equal to 0.005.
4. A process according to any one of claims 1 to 3 characterised in that the basic polymer material comprises a polyolefin.
5. A process according to claim 4 characterised in that the basic polymer material is formed for a major part of styrene and the swelling additive composition essentially contains methyl methacrylate.
6. A process according to any one of claims 1 to 5 characterised in that the basic polymer material comprises a polyurethane.
7. A process according to claim 6 characterised in that the basic polymer material results in respect of the major part thereof from the reaction of a composition comprising at least one isocyanate and at least one polyol, and the swelling additive composition essentially contains styrene.
8. A process according to either one of claims 6 and 7 characterised in that the basic polymer material comprises both a polyurethane and a monomer such as an allylic, acrylic or methacrylic monomer.
9. A process according to any one of claims 1 to 8 characterised in that the basic polymer material also contains a product for joining its matrix to that of the swelling additive composition.
10. A process according to claim 1 characterised in that the refractive index gradient develops in a transverse direction with respect to that along which the selling action occurs.

Images